A further increase in nitrogen (N) intensive biomass supplies to substitute fossil carbon sources implies inclusion of additional reactive nitrogen (Nr) into the biosphere. A Danish model study compared low-intensity managed seminatural beech forest and a winter wheat system with respect to N losses and greenhouse gas (GHG) emissions. Losses of reactive N to air and groundwater per unit of energy produced were four to six times higher for the winter wheat system. The energy efficiency was an order of magnitude higher in the forest system, whereas the related GHG emission reduction by fossil coal substitution differed by